LUBBOCK, Texas — A university professor was arrested Wednesday for allegedly telling authorities that 30 vials of plague were missing when he knew they had been destroyed, the U.S. attorney's office said.

The mysterious episode at Texas Tech University triggered a terrorism-alert plan and showed how jittery Americans are over the threat of a biological attack.

Dr. Thomas C. Butler, chief of the infectious diseases division of the department of internal medicine, was arrested late Wednesday on a complaint of making a false statement to a federal agent.

U.S. Attorney Dick Baker said the professor said the vials were missing as of Saturday when "truth in fact, as he well knew, he had destroyed them prior to that."

The samples, about 30 of the 180 the school was using for research on the treatment of plague, were reported missing to campus police Tuesday night.

Baker said FBI agents interviewed Butler on Tuesday. He wouldn't say whether Butler made the initial report or comment on why the vials were destroyed.

Butler, who has been at Texas Tech since 1987, was jailed pending his arraignment set for Thursday.

Earlier Wednesday, the FBI had only said it had accounted for the vials. An FBI official in Washington, speaking on condition of anonymity, had said authorities believed the samples of the lethal bacteria were simply destroyed and not properly accounted for, rather than stolen or misplaced.

"We have accounted for all those missing vials and we have determined that there is no danger to public safety whatsoever," FBI agent Lupe Gonzalez said at a news conference in Lubbock.

Plague — along with anthrax, smallpox and a few other deadly agents — is on a watch list distributed by the government, which wants to make sure doctors and hospitals recognize a biological attack quickly.

Health officials say 10 to 20 people in the United States contract plague each year, usually through infected fleas or rodents. The plague can be treated with antibiotics, but about one in seven U.S. cases is fatal.

Texas Tech said that officials thought it was "prudent" to get law enforcement involved because of current concerns about bioterrorism.

The FBI sent agents to Lubbock. The Centers for Disease Control and Prevention also took part in the investigation. Homeland Security chief Tom Ridge contacted Lubbock's mayor. About 60 investigators from the FBI and other agencies converged on the medical school Tuesday night.

A post-Sept. 11 emergency plan was activated, under which Lubbock-area hospitals and medical personnel were notified to be on the lookout for cases of plague. But the public was not told about the incident until late Wednesday morning.

"We didn't want to spread panic," Texas Tech Chancellor David Smith said. "As it turns out, they were never missing." He would not elaborate.

The vials were kept in an area with limited access but without a surveillance camera, officials said.

Mayor Marc McDougal said the public was not notified because of information the university received late Tuesday that indicated the missing vials were not a threat to the public.

"I think when you look how quickly it came down and how it got resolved, I think it would be hard to second guess" how we handled it, he said. "One thing we didn't want to do was cause people to panic."

The form of the disease called bubonic plague is not contagious. But left untreated, it can transform into the more dangerous pneumonic plague that can be spread person to person.

The most infamous plague outbreak began in 1347 and killed 38 million people in Europe and Asia within five years.